1. Field
One or more embodiments of the present invention relate to a method, medium and system providing an image signal, and more particularly, to a method, medium and system reducing a color error band caused by a drastic brightness difference between sub-pixels by using a weight allocated according to the period of change in pixel values in an image display system such as a liquid crystal display (LCD), a plasma display panel (PDP), a light-emitting diode (LED), or an organic light emitting diode (OLED).
2. Description of the Related Art
In techniques of representing the relationship between colors, color spaces are used. Different image processing systems may use different color spaces for various reasons. Most image signal display apparatuses such as color cathode ray tube (CRT) monitors, liquid crystal display (LCD) monitors, and plasma display panel (PDP) monitors adopt a Red-Green-Blue (RGB) color space.
An RGB color space comprises red (R), green (G), and blue (B) which are three primary colors that can be added to one another. A plurality of spectral elements of each of R, G, and B are additively mixed, thereby generating other colors.
An RGB color model can be represented as a three-dimensional (3D) cube with the color black being located at the origin of the 3D cube, and white being opposite of black. For example, a 24-bit color graphic system providing eight bits for each color channel represent R as (255, 0, 0).
An RGB color model can facilitate the design of computer graphic systems, but is not suitable for every application because it depends too much on the relationship between R, G, and B. Various image processing techniques such as histogram smoothing are performed simply based on grayscale. Therefore, RGB images often need to be converted into grayscale images. According to the National Television Systems Committee standard, an RGB image can be converted into a grayscale image using Equation 1, for example.Y=0.288R+0.587G+0.114B  Equation 1
Of R, G, and B, the color G affects grayscale the most. Thus, G grayscale can be used alone as grayscale data. Due to this characteristic, a G component is generally located at the center of each pixel in a sub-pixel-based display device. Therefore, a plurality of sub-pixels of each pixel may be arranged in the order of R, G, and B components or B, G, and R components.
The field of RGB sub-pixel-based image rendering techniques is largely divided into the field of resolution improvement techniques and the field of pixel error correction techniques. Examples of the resolution improvement techniques include an image display technique discussed in U.S. Pat. No. 6,823,088 to Mitsubishi Corporation that involves providing a pixel driving mode and a sub-pixel driving mode and generating image data with the use of a controller, and a resolution improvement filter technique discussed in U.S. Published Patent Application No. 2004-80479 to Clair Voyante Corporation, that involves the use of a resampling filter.
Examples of the pixel error correction techniques include a technique discussed in U.S. Pat. No. 6,756,992 to Mitsubishi Corporation that involves providing a font database, magnifying an image three times, and sub-sampling the magnified image, and a technique discussed in U.S. Published Patent Application No. 2003-214513 to Microsoft of removing jagging from text.
FIG. 1 is a diagram for explaining the displaying of alphabet letter ‘A’ using an RGB sub-pixel-type display device. Referring to FIG. 1, each pixel includes a plurality of R, G, and B sub-pixels 11. Each of the R, G, and B sub-pixels 11 of each pixel may have a value. The combination of the values of the R, G, and B sub-pixels 11 of each pixel can represent various colors. The R, G, and B sub-pixels 11 of each of a plurality of black pixels 12 that form alphabet letter ‘A’ may all have a value of 0. Since the R, G, and B sub-pixels 11 of each pixel occupy different spaces, they may fail to blend precisely. This problem with sub-pixel blending is apparent at the boundary between a pair of adjacent pixels, and particularly, when the size of pixels is too large. For example, left edges of alphabet letter “A” formed by the black pixels 12 may become bluish because of B sub-pixels 11 that adjoin the left sides of the black pixels 12.
FIG. 2 explains a color error band. Referring to FIG. 2, due to the properties of the human vision, color error bands 21 and 22 may be generated along the edges of an object in an image where the brightness of the image drastically changes. The color error bands 21 and 22 cause distortions in the intensity of an actual image signal. In general, the larger the size of the pixels, the clearer the color error bands 21 and 22 become.